The present invention relates to an endless traction band for a snowmobile. Such a traction band is designed to travel on snow, on which the use of wheeled vehicle is of little help.
A traction band is usually made of a reinforced molded rubber material, having longitudinally spaced and transversely disposed stiffeners embedded in the rubber material. The endless band is flexible around a lateral axis so that it can follow the curvature around drive and idler sprocket wheels. It is designed to support a significant portion of the total weight of the vehicle and apply a traction force on the ground.
The body of the traction band has a ground-engaging outer side or surface and an inner surface. The inner surface cooperates with a suspension system and delimits the required space for the powering system, like for instance the sprocket wheel and the idler wheel. Along the circumference of the inner surface, two rows of holes generally cooperates with the teeth of the corresponding sprocket wheels and idler wheels or alternatively, those wheels may mesh with driving lugs that are inwardly projecting from the inner side of the band.
The ground-engaging outer side usually has a sequence of profiles that is repeated uniformly over the total length of the traction band. Each sequence of profiles or tread pattern comprises laterally extending profiles that are longitudinally spaced apart by flat areas. Each profile comprises a series of outwardly projecting traction lugs. The choice of lug profiles that are selected to be part of every sequence of profiles, which is repeated along the circumference of the traction band, has an influence on the band behavior on the snow, on the snowmobile performances and on the comfort of the driver. These criteria are very critical in a marketing point of view, since they differentiate products from one another in the eye of a potential customer.
There is always a need for a traction band which enhances the driver-s comfort during a snowmobile ride. As the band reaches certain rotation speeds, the vibration and noise levels can sometimes cause inconveniences to the drivers and the people who are near.
In the prior art, Lecours (U.S. Pat. No. 5,709,440) proposes a snowmobile traction band which he states procures a reduced operation noise, due to the non-uniform arrangement of the traction elements in the tread pattern. Lecours suggests that certain of the external traction lug profiles be spaced non-uniformly in the longitudinal direction of the traction band. However, this suggestion is not practical in respect of snowmobiles using sprocket wheels.
Courtemanche (U.S. Pat. No. 5,722,745) has also addressed that problem by proposing an endless rubber traction band for a snowmobile with what he calls a noise reducing tread pattern. This invention consist of a thread pattern repeated all over the traction band, each comprising the same three successive lug profiles. However, notwithstanding the promised noise reduction, in reality, the noise reduction achieved by Courtemanche is limited if present.
With this invention, the level of noise and vibrations are greatly diminished because no sequence of profiles is repeated along the traction band more than once along its outside circumference. The noise and vibration amplitudes are therefore more optimally broken as the band rotates.